Production of electrolytic cathode-diaphragm structures



K. E. STUART June 28, 1932.

PRODUCTION OF ELECTROLYTIC CATHODE DIAPHRAGM STRUCTURES Filed Jan. 31, 1950 3 Sheets-Sheet 1 grvue'nto'o June 28, 1932. E RT 1,865,152

PR ODUCTION OF ELECTROLYTIC CATHODE DIAPHRAGM STRUCTURES Filed Jan. 31, 1930 3 Sheets-Sheet 2 June 28, 1932. K. E. STUART PRODUCTION OF ELECTROLYTIC CATHODE DIAPHRAGM STRUCTURES Fil ed Jan. 51, 19:50 5 Sheets-Sheet 3 Patented J 1932 UNITED STATES PATENT OFFICE KENNETH E. STUART, OF N IAGABA FALLS, NEW YORK, ASSIGNOB TO HOOKER ELECTRO- CHEMICAL COMPANY, OF NEW YORK, N. Y., A CORPORATION 0! NEW YORK PRODUCTION OI ELECTROLYTIC CATHODE-DIA PHRAGM STRUCTURES Application filed January 31, 1080; Serial No. 425,001.

This invention relates to a method for the production of porous diaphragms for electrolytic cells and particularly to diaphragms of fibrous material. It has for its object the provision of an inexpensive method of applying such diaphragms to perforated cathode plates and particularly when such plates are of irregular, warped or non-cylindrical, nonplanar form, in such manner that there shall be no joints orseams in such diaphragms. In my application Serial No. 275.860, filed Ma 7, 1928, I have disclosed a method in which this object is accomplished by starting with the fibrous raw material, such as asbestos fiber, instead of using paper made from the same fiber, as has heretofore been customar and is carried out by immersing such catho e in a tank filled with pulp formed by maintaining the fibrous material in suspension, preferably in water, and by drawing the water through the perforations, preferably by applying vacuum to the reverse side.

I have further discovered that the same object may be advantageously accomplished bysuspending the fibrous material in a liquid medium of such specific ravity with respect to the fibrous material that the material remains in suspension sufficiently long to permit the deposition operation to be effected without the necessit for using any other means, such as jets 0 water, for keeping the material in suspension. It should be observed that if the liquid medium be of a gravity much lighter than that of the fibrous material the latter will sink rapidly to the bottom; and similarly if the liquid medium be of a gravity much heavier, than that of the fibrous material the latter will rise rapidly to the, top. In neither case would the desired result .be accomplished. It is necessary therefore that the gravity otthe liquid medium be so adjusted to that of the fibrous materialthat the latter, after having been thoroughly distributed through it, will rise or settle so slowly that there is am le time for the operation of depositing the diaphragm before there has been any appreciable displacement of the fibrous material in the medium of suspension. Asv such movement is retarded by the viscosity of the liquid, any addition to the liquid within the desired limits.

that tends toincrease its viscosity aids in the desired result. As asbestos is the preferred fibrous material, and as this is heavier than water, in practice I prefer to use a medium of suspension that is likewiseheavier than water, and this can be most readily secured by adding to the water soluble salts in the right proportion, since by varying the proportion of such salts to the water, the gravlty ot' the solution can be regulated- It is obvious'that there exists a great variety of salts that would be suitable for this purpose, but in cases where common salt is the raw material fed to the cell and sodium hydroxide one of the products formed, the use of these two salts introduces nothing into the cell that is not normally found there. If the cell were 'used for the production of potassium hydroxide, this would naturally be substituted for sodium for the purposes mentioned.

In carrying out the method of the present invention the cathode plates are immersed 1n a tank filled with a suspension of a fibrous material, such as asbestos fiber,-in a liquid medium of substantially greater specific gravity, and preferably also of greater viscosity than water, such as, for example, an aqueous solution of common salt or sodium hydroxide or both. The li uid medium is then forced through the per orations in the plate, preferably by applying vacuum to the reverse side, whereby the fibers are deposited upon the surface so as to form an unbroken seamless coating of fibrous material of any desired thickness. l

The accompanying drawings will serve as an illustration of a method of putting my invention into practice.

Fig. 1 is a plan view of a cathode plate of the character described and provided with prgjecting portions or fingers.

ig. 2 is a sectional end elevation on theline 2+2 of Fig. 1.

Fig. 3 is a general view in plan showing the pulp tank with cathode plate in position and the means for applying vacuum to it and for removal of the water drawn through the perforations.

' Fig. 4 is a sectional, elevation of the pulp I SKIS draining and C) in position for inspect-ion and removal.

Fig. 6 is a sectional end elevation of a modified form of pulp tank adapted for depositingi a diaphragm upon a flat cathode plate of or v ina-ry form. Referring to Figs. 1 and 2: 1 is the active perforated surface of the cathode 2 and as shown is formed .with a fiat portion having hollow rectangular members o'r fingers 3 projecting at right angles to the rated sheet metal, but

flat surfacet. mg b i d f f rejecting ers ma e orme per 0- p I for reasons that will be stated more fully later, I prefer to use woven wire screen as illustrated in Fig.2. The

active perforated portion of this cathode is supported by a non-perforated back 4 of box section havmg the flanges 5 adapted to be clamped a ainst the side of the cell body (not shown). is box section which remains outside the cell serves to receive the catholyte, such as caustic soda or potash, also the gaseous product formed upon the cathode, such as hydrogen. The projecting fingers 3 may be reinforced by any suitable structure such as 6.

Referring to Figs. 3, 4, 5 and 6, 7 is the pulp tank above referred to of rectangular form and of such dimensions as to adapt it to receive thecathode 2 with the fingers 3 hangvertically downward and the flanges 5 resting upon the upper edges of the side and end walls, the fingers 3 being preferably symmetrically spaced between said side walls. 8 is a-false bottom forming an inverted V, the peak of which is substantially central and the sides of which form with the side walls of the tank valleys in which maybe housed the pipes 9. These are referably in sections, eight to each side. ach pair -of pipes is jo ned in a common T, each pair of Ts is jloined in a common header, each pair of eaders is joined to a common feeder, and the two feeders are joined in a common ipe 10 which passes through the side wall 0 the tank and 1s controlled by the valve 11. In this way all sections of the pipe 9 are served exactly alike. The pipes 9 are perforated in two rows. One row of perforations is preferably directed upward and the other row of perforations is directed in a line substantially parallel with the false bottom 8. These perforations are for the purpose of admitting and directing air used for agitating the ulp in order to bring it into substantially uni orm suspension in the liquid medium. The Ts,

Both the fiat surface and the headers, geeders, etc., are housed between the false bot om 8 and the true bottom 12 of the tank 7. v

13 is a large closed tank which may be of cylindrical form, resting upon one side, and must be adapted to withstand vacuum, and of a size sufiicient to receive the water drawn through the wire screen of the cathode. The tank 13 is connected to the non-perforated back 5 of the cathode through the valve 14, pipes 15 and 16, swing joints 17, pipes 18, swing joints 19 and pipes 20.

The tank 13 may be put in connection either with a vacuum pump (not shown) through the valve 21 and pipe 22, or with a pressure pump (not shown) through valve 23 and ipe 24. The gauge 25 serves to indicate the egree of vacuum or pressure applied to the tank 13. The pipe 26 isv connected to the tank 13 at a predetermined distance above the bottom and is controlled by the valve 27. The pipe 28 is connected to the bottom of the tank 13 and leads thence over the side of the tank 7 It is controlled by the valve 29.

The pipe 18 may be raised and lowered by the chain hoist 30, pivoting-about the swin joints 17. The cathode 2 may be raised an lowered by the chain hoist 31, the pipes 20 pivoting about the swing joints 19.

.The operation of the process is as follows:

A mixture of asbestos fiber with a saturated solution of sodium chloride containing a small amount of sodium hydroxide for example, fifty grams per liter) is placed in tank 7. The cathode is lowered into position A and air is blown into tank 7 through valve 11, pipe 10, and perforated pipes 9 until the fiber is thoroughly suspended in the liquid medium.

The air is then cut oil" by closing valve 11 and suction applied to the interior of the cathode structure by connectingit with tank 13 through valve 14, and building up a vacuum in tank 13 by means of a source of vacuum connected through. pipe 22 and valve 21.

As soonas a sufliciently thick layer of asbestos has been deposited on the cathode surface, the cathode structure is lifted out of the tank 7, being prevented from touching the sides by proper coordination between the lift of the two hoists 30 and 31. When clear of the splash top 32 the cathode is lifted into position B. In this position all of the liquid is drained out of the cathode. The vacuum is allowed to act upon the diaphragm for 351! The presence of a small amount of sodium hydroxide in the suspension medium is of advantage not only in raising the specific gravity and viscosity of the liquid, but also exercises a deflocculating effect upon the fibers and gives a smoother deposit. It also neutralizes the tendency of the brine to causerusting of the iron wires composing the active surface of the cathode.

Both the sodium chloride and the sodium hydroxide used in the suspension medium given by way of example also have an advantageous agglutinating effect in the prepared diaphragm. On drying or partially drying the prepared diaphragm the sodium hydroxide imparts toughness to the (baphragm layer, while the salt imparts a surface hardness. Both of these ingredients thus play an important part in rendering the prepared cathode-diaphragm structure moreresistant to the wear and tear of handling in storage and in the construction of cells therefrom.

I prefer to make the active perforated plate of woven wire screen rather than of perforated sheet metal as the wires give a better bond for the fibers and, besides, afford a greater area of active surface owing to their corrugation and exposed sides.

Fig. 6 shows a modified form of tank 7 adapted for applying diaphragms by this method to an ordinary flat cathode plate.

My invention is not limited, however, to the particular embodiments illustrated in the drawings, but comprises broadly a method of making electrolytic cathode-diaphragm structures wherein a fibrous material, such as asbestos fiber, is deposited on the active perforated surface of a cathode structure, by bringing a suspension of the fibrous material in a liquid of substantially greater specific gravity than water into contact with the active perforated surface of the cathode, and by the application of differential pressure forcing the liquid of the suspension through the perforations of the active surface.

It is also of advantage if, as is usually the case, the liquid medium has a greater viscosity than that of water; and the presence of a substance having a deflocculating effect on the fibers is also desirable.

I claim:

1. A method of making electrolytic cathode diaphragm structures which comprises immersing the active perforated surface of an electrolytic cathode in a suspension of a fibrous material in an aqueous solution of substantially greater viscosity than water, and forcing the liquid of the suspension through the perforations of said surface by the use of a differential pressure.

2. A method of making electrolytic cathode diaphragm structures which comprises bring: ing a suspension of asbestos fiber in a saturated solution of sodium chloride, into contact with the active perforated surface of an electrolytic cathode, and forcing the li uid of the suspension through the perforations of said surface by the use of a differential pressure.

3. A method of making electrolytic cathode diaphragm structures which comprises bringing a suspension of asbestos fiber in a saturated solution of sodium chloride containing a small amount of sodium hydroxide, into contact with the active perforated surface of an electrolytic cathode, and forcing the liquid of the suspension through the perforations of said surface by the use of a differential pressure.

4. A method of making electrolytic cathode diaphragm structures which comprises bringing a suspension of asbestos fiber in a saturated solution of sodium chloride, into contact with the active perforated surface of an electrolytic cathode-having a warped active surface, and forcing the liquid of the suspension through the perforations of said surface by the application of suction to the interior of said cathode.

' 5. A method of making an electrolytic cathode diaphragm which comprises immersing the active perforated surface of an electrolytic cathode in a suspension of a fi rous material in a liquid medium .and applying differential pressure to the two sides of said cathode, said medium being of such specific gravity with respect to the specific gravity of said fibrous material that said fibrous material will remain suspended in it without agitation for a period of time substantially longer than the time required to deposit a diaphragm of the desired thickness upon said cathode.

6. Amethod of making an electrolytic cathode diaphragm which comprises immersing the active perforated surface of an electrolytic cathode in a suspension of a fibrous material in a liquid medium and applying differential pressure to the two sides of said cathode, said medium being of such specific gravity with respect to the specific gravity of said fibrous material and of such viscosity that said fibrous material will remain suspended in it without agitation for a period of time substantially longer than the time required to deposit a diaphragm of the desired thickness upon said cathode.

7. A method of making electrolytic cathode diaphragm structures which comprises immersing the active perforated surface of an electrolytic cathode in a suspension of a fibrous material in an aqueous solution of substantially greater specific ravity than water and forcing the liquid of the suspension through the perforations face by the use of a differential pressure.

8. A method of making electrolytic cathode diaphragm structures which comprises immersing the active perforated surface of an electrolytic cathode in a suspension of a of said surfibrous material in an aqueous solution of substantially greater specific gravity than water and containing a deflocculating agent, and forcing the liquid of the suspension through the perforations of said surface by the use of a differential pressure.

9. A method of making electrolytic cathode diaphragm structures which comprises immersing the active perforated surface of an electrolytic cathode, having a warped active surface, in a suspension of a fibrous material in an aqueous solution of substantially greater specific gravity than water, and forcing the liquid of the suspension through the perforations of said surface by the use of a differential pressure.

10. A method of making electrolytic cathode diaphragm structures which comprises immersing the active perforated surface of an electrolytic cathode, having a warped active surface, in a suspension of a fibrous material in an aqueous solution of substantially greater specific gravity than water, and toreing the liquid of the suspension through the perforations of said surface by the application of suction to the interior of said cathode.

KENNETH E. STUART.

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